116 TRANSACTIONS OF THE PLYMOUTH INSTITUTION. 
the great plateau of the Lizard was not composed of stratified 
rocks." 
Sir Henry De la Beche, fifty years ago, summed up as follows : 
"As a whole, however, the hornblende slate and rock seem to 
have formed a basin into which the serpentine and diallage rock 
have been poured in a state of fusion. " 
For nearly forty years after De la Beche's Report, little further 
light was cast on this interesting series of metamorphic rocks, 
until Professor Bonney published his paper on "The Serpentine 
and Associated Rocks of the Lizard District," in the Quarterly 
Journal of the Geological Society, in 1877. This was followed 
by a second paper on "The Hornblendic and Other Schists of 
the Lizard District, with some Additional Notes on the Serpen- 
tine," published in the same journal in 1883. These papers 
marked a new departure in the history of the investigation. 
They treated minutely of the various junctions between Polurrian 
on the west coast, and Porthallow on the east coast, and the 
macroscopical and microscopical description and chemical com- 
position of the rocks were given. 
Professor Bonney's observations led him to conclude that — 
1. The serpentine of the Lizard was originally an intrusive 
rock. 
2. Its intrusion was posterior to the metamorphism of the 
hornblende schist. 
3. The serpentine had been broken through by several granite 
dykes, by gabbros of two dates, and by dark trap dykes. 
4. The gabbros were liable to three forms of mineral change ; 
(a) a gradual conversion of felspar into a micro-crystalline saus- 
suritic mineral ; (b) conversion of their diallage into hornblende 
by pseudomorphism or re-crystallization, some olivine disappearing 
in the process ; (c) conversion of the olivine into serpentine. 
5. The trap dykes were probably all once dolerites, or basalts, 
and the hornblende was due to the metamorphism of the original 
pyroxenic constituent. 
6. The metamorphism of the serpentine was probably complete 
before the intrusion of the above rocks. 
7. The serpentinous aspect of a rock was often illusory, and 
due to the presence of extremely small proportions of that 
mineral. 
8. In addition to the talco-micaceous and hornblende-schist 
